Method for generating and building support structures with deposition-based digital manufacturing systems

ABSTRACT

A method for generating data for a support structure to be built with a deposition-based digital manufacturing system, the method comprising generating a convex hull polygon based on a boundary polygon of a layer of the support structure, offsetting the convex hull polygon inward, offsetting the boundary polygon outward, and generating an intersection boundary polygon based at least in part on the offset boundary polygon and the offset convex hull polygon.

BACKGROUND

The present disclosure relates to direct digital manufacturing systemsfor building three-dimensional (3D) models. In particular, the presentinvention relates to techniques for generating support structures foruse with 3D models in deposition-based digital manufacturing systems.

A deposition-based digital manufacturing system, such as anextrusion-based system or a jetting-based system, is used to build a 3Dmodel from a digital representation of the 3D model in a layer-by-layermanner by extruding a flowable consumable modeling material. Forexample, in extrusion-based systems, the modeling material is extrudedthrough an extrusion tip carried by an extrusion head, and is depositedas a sequence of roads on a substrate in an x-y plane. The extrudedmodeling material fuses to previously deposited modeling material, andsolidifies upon a drop in temperature. The position of the extrusionhead relative to the substrate is then incremented along a z-axis(perpendicular to the x-y plane), and the process is then repeated toform a 3D model resembling the digital representation.

Movement of the extrusion head with respect to the substrate isperformed under computer control, in accordance with build data thatrepresents the 3D model. The build data is obtained by initially slicingthe digital representation of the 3D model into multiple horizontallysliced layers. Then, for each sliced layer, the host computer generatesone or more tool paths for depositing roads of modeling material to formthe 3D model.

In fabricating 3D models by depositing layers of a modeling material,supporting layers or structures are typically built underneathoverhanging portions or in cavities of objects under construction, whichare not supported by the modeling material itself. A support structuremay be built utilizing the same deposition techniques by which themodeling material is deposited. The host computer generates additionalgeometry acting as a support structure for the overhanging or free-spacesegments of the 3D model being formed. Support material is thendeposited from a second nozzle pursuant to the generated geometry duringthe build process. The support material adheres to the modeling materialduring fabrication, and is removable from the completed 3D model whenthe build process is complete.

SUMMARY

A first aspect of the present disclosure is directed to acomputer-implemented method for generating data for a support structureto be built with a deposition-based digital manufacturing system. Themethod includes providing a boundary polygon of a layer of the supportstructure, generating a convex hull polygon based on the boundarypolygon, offsetting the convex hull polygon inward, and offsetting theboundary polygon outward. The method also includes generating anintersection boundary polygon based at least in part on the offsetboundary polygon and the offset convex hull polygon.

Another aspect of the present disclosure is directed to acomputer-implemented method for generating data for a support structureto be built with a deposition-based digital manufacturing system, wherethe method includes providing vertices defining a boundary polygon for alayer of the support structure, and generating vertices of a convex hullpolygon based on the vertices of the boundary polygon. The method alsoincludes offsetting the vertices of the convex hull polygon inward toprovide an offset convex hull polygon, and offsetting the vertices ofthe boundary polygon outward to provide an offset boundary polygon. Themethod further includes generating an intersection boundary polygonhaving vertices, wherein at least a portion of the vertices of theintersection boundary polygon are selected from the group consisting ofa vertex that is located at an intersection of the offset boundarypolygon and the offset convex hull polygon, a vertex of the offsetboundary polygon located inside of the offset convex hull polygon, avertex of the offset convex hull polygon located inside of the offsetboundary polygon, and combinations thereof.

Another aspect of the present disclosure is directed to a method forbuilding a support structure with a deposition-based digitalmanufacturing system. The method includes generating a convex hullpolygon based on a boundary polygon for each of a plurality of layers ofthe support structure, offsetting the convex hull polygon inward foreach of the plurality of layers, and offsetting the boundary polygonoutward for each of the plurality of layers. The method also includesgenerating an intersection boundary polygon for each of the plurality oflayers based at least in part on the offset boundary polygon and theoffset convex hull, and generating a tool path for each of the pluralityof layers based at least in part on the intersection boundary polygon.The method further includes transmitting the generated tool paths to thedeposition-based digital manufacturing system, and building the supportstructure based at least in part on the transmitted tool paths, wherethe support structure has substantially convex dimensions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an extrusion-based digital manufacturingsystem for building 3D models and support structures, where the supportstructures are generated pursuant to a support structure generationtechnique of the present disclosure.

FIG. 2 is a flow diagram of a method for generating data of a 3D modeland a corresponding support structure.

FIG. 3 is a flow diagram of a method for generating a layer of thesupport structure pursuant to the support structure generation techniqueof the present disclosure.

FIGS. 4A-4H are top views of a first layer of the support structure,illustrating an application of the method shown in FIG. 3.

FIGS. 5A-5H are top views of a second layer of the support structure,further illustrating the application of the method shown in FIG. 3,where the second layer is located below the first layer shown in FIGS.4A-4H.

FIGS. 6A-6H are top views of a third layer of the support structure,further illustrating the application of the method shown in FIG. 3,where the third layer is located below the second layer shown in FIGS.5A-5H.

DETAILED DESCRIPTION

The present disclosure is directed to a support structure generationtechnique that generates support structures for use with 3D models. Forexample, the support structures may be generated underneath overhangingportions or in cavities of the 3D models under construction, which arenot supported by modeling material itself. As discussed below, thetechnique generates a support structure having convex outer dimensionsthat reduce in size and complexity in a downward direction along avertical axis. This reduces the size of the support structure andreduces the distance and angular deflection required by a depositionhead to move around the perimeter of the support structure.Additionally, as discussed below, the technique may also reduce the sizeof interior voids in the support structure, thereby reducinginterruptions when bulk filling the interior regions of the supportstructure (e.g., with a raster fill pattern). These arrangements reducethe overall time required to build the support structure in adeposition-based digital manufacturing system.

FIG. 1 is a front view of system 10 in use with computer 12, wheresystem 10 is deposition-based digital manufacturing system that may beused to build 3D models with support structures generated pursuant tothe technique of the present disclosure. Suitable deposition-baseddigital manufacturing systems include extrusion-based systems, such asfused deposition modeling systems developed by Stratasys, Inc., EdenPrairie, Minn., and jetting-based systems.

Computer 12 is one or more computer-based systems that communicates withsystem 10, and may be separate from system 10, or alternatively may bean internal component of system 10. As discussed below, computer 12 maygenerate data, such as tool paths, for building 3D models and supportstructures in a layer-by-layer manner, where computer 12 may generatethe layers of the support structures pursuant to the support structuregeneration technique of the present disclosure.

In the shown embodiment, system 10 is an extrusion-based system thatincludes build chamber 14, platen 16, gantry 18, extrusion head 20, andsupply sources 22 and 24. Build chamber 14 is an enclosed, heatableenvironment that contains platen 16, gantry 18, and extrusion head 20for building a 3D model (referred to as 3D model 26) and a correspondingsupport structure (referred to as support structure 28). Platen 16 is aplatform on which 3D model 26 and support structure 28 are built, andmoves along a vertical z-axis based on signals provided from controller30. As discussed below, controller 30 may direct the motion of platen 16and extrusion head 20 based on data supplied by computer 12.

Gantry 18 is a guide rail system configured to move extrusion head 20 ina horizontal x-y plane within build chamber 14 based on signals providedfrom controller 30. The horizontal x-y plane is a plane defined by anx-axis and a y-axis (not shown in FIG. 1), where the x-axis, the y-axis,and the z-axis are orthogonal to each other. In an alternativeembodiment, platen 16 may be configured to move in the horizontal x-yplane within build chamber 14, and extrusion head 20 may be configuredto move along the z-axis. Other similar arrangements may also be usedsuch that one or both of platen 16 and extrusion head 20 are moveablerelative to each other.

Extrusion head 20 is supported by gantry 18 for building 3D model 26 andsupport structure 28 on platen 16 in a layer-by-layer manner, based onsignals provided from controller 30. Accordingly, controller 30 alsodirects extrusion head 20 to selectively deposit the modeling andsupport materials based on data supplied by computer 12. In theembodiment shown in FIG. 1, extrusion head 20 is a dual-tip extrusionhead configured to deposit modeling and support materials from supplysource 22 and supply source 24, respectively.

Examples of suitable extrusion heads for extrusion head 20 include thosedisclosed in LaBossiere, et al., U.S. Patent Application PublicationNos. 2007/0003656 and 2007/00228590; and Leavitt, U.S. PatentApplication Publication No. 2009/0035405. Alternatively, system 10 mayinclude one or more two-stage pump assemblies, such as those disclosedin Batchelder et al., U.S. Pat. No. 5,764,521; and Skubic et al., U.S.Patent Application Publication No. 2008/0213419. Furthermore, system 10may include a plurality of extrusion heads 18 for depositing modelingand/or support materials.

The modeling material may be provided to extrusion head 20 from supplysource 22 through pathway 32. Similarly, the support material may beprovided to extrusion head 20 from supply source 24 through pathway 34.System 10 may also include additional drive mechanisms (not shown)configured to assist in feeding the modeling and support materials fromsupply sources 22 and 24 to extrusion head 20.

The modeling and support materials may be provided to system 10 in avariety of different media. For example, the modeling and supportmaterials may be provided as continuous filaments fed respectively fromsupply sources 22 and 24, as disclosed in Swanson et al., U.S. Pat. No.6,923,634; Comb et al., U.S. Pat. No. 7,122,246; and Taatjes et al, U.S.patent application Ser. Nos. 12/255,808 and 12/255,811. Examples ofsuitable average diameters for the filaments of the modeling and supportmaterials range from about 1.27 millimeters (about 0.050 inches) toabout 2.54 millimeters (about 0.100 inches), with particularly suitableaverage diameters ranging from about 1.65 millimeters (about 0.065inches) to about 1.91 millimeters (about 0.075 inches). Alternatively,the modeling and support materials may be provided as other forms ofmedia (e.g., pellets and resins) from other types of storage anddelivery components (e.g., supply hoppers and vessels).

Suitable modeling materials for building 3D model 26 include materialshaving amorphous properties, such as thermoplastic materials, amorphousmetallic materials, and combinations thereof. Examples of suitablethermoplastic materials include acrylonitrile-butadiene-styrene (ABS)copolymers, polycarbonates, polysulfones, polyethersulfones,polyphenylsulfones, polyetherimides, amorphous polyamides, modifiedvariations thereof (e.g., ABS-M30 copolymers), polystyrene, and blendsthereof. Examples of suitable amorphous metallic materials include thosedisclosed in U.S. patent application Ser. No. 12/417,740.

Suitable support materials for building support structure 28 includematerials having amorphous properties (e.g., thermoplastic materials)and that are desirably removable from the corresponding modelingmaterials after 3D model 24 and support structure 26 are built. Examplesof suitable support materials include water-soluble support materialscommercially available under the trade designations “WATERWORKS” and“SOLUBLE SUPPORTS” from Stratasys, Inc., Eden Prairie, Minn.; break-awaysupport materials commercially available under the trade designation“BASS” from Stratasys, Inc., Eden Prairie, Minn., and those disclosed inCrump et al., U.S. Pat. No. 5,503,785; Lombardi et al., U.S. Pat. Nos.6,070,107 and 6,228,923; Priedeman et al., U.S. Pat. No. 6,790,403; andHopkins et al., U.S. patent application Ser. No. 12/508,725.

During a build operation, controller 30 directs one or more drivemechanisms (not shown) to intermittently feed the modeling and supportmaterials to extrusion head 20 from supply sources 22 and 24. For eachlayer, controller 30 then directs gantry 18 to move extrusion head 20around in the horizontal x-y plane within build chamber 14 based on thedata (e.g., tool paths) generated by computer 12. The received modelingand support materials are then deposited onto platen 16 to build thelayer of 3D model 26 and support structure 28 using the layer-basedadditive technique.

The formation of each layer of 3D model 26 and support structure 28 maybe performed in an intermittent manner in which the modeling materialmay initially be deposited to form the layer of 3D model 26. Extrusionhead 20 may then be toggled to deposit the support material to form thelayer of support structure 28. The reciprocating order of modeling andsupport materials may alternatively be used. The deposition process maythen be performed for each successive layer to build 3D model 26 andsupport structure 28.

Support structure 28 is desirably deposited to provide vertical supportalong the z-axis for overhanging regions of the layers of 3D model 26.As shown in FIG. 1, the successive layers of support structure 28 havereduced areas and complexities in the horizontal x-y plane when movingin a downward direction along the vertical z-axis, and provide convexdimensions. The reduced areas correspondingly reduce the distance thatextrusion head 20 is required to move around the lateral perimeter of agiven layer of support structure 28, and as well as lowering therequired total angular deflection of extrusion head 20. The reduce totalangular deflection correspondingly allows extrusion head 20 to negotiatecorners without needing to slow down. After the build operation iscomplete, the resulting 3D model 26/support structure 28 may be removedfrom build chamber 14, and support structure 28 may be removed from 3Dmodel 26.

FIG. 2 is a flow diagram of method 36 for generating data of a 3D modeland corresponding support structure with computer 12, where thegenerated data may be subsequently used to build the 3D model andsupport structure in a deposition-based digital manufacturing system(e.g., system 10). Method 36 is an example of a suitable method thatincorporates the support structure generation technique of the presentdisclosure for generating support structures having convex dimensions.The following discussion of method 36 is made with reference to 3D model26 and support structure 28 (shown in FIG. 1). However, method 36 isapplicable for building 3D models and corresponding support structureshaving a variety of different geometries, and with a variety ofdifferent deposition-based digital manufacturing systems.

As shown, method 36 includes steps 38-52, and initially involvesreceiving a digital representation of 3D model 26 at computer 12 (step38). Upon receipt of the digital representation of 3D model 26, computer12 may reorient the digital representation and slice the digitalrepresentation into multiple layers (step 40). As discussed below,computer 12 may then generate one or more layers of support structure28, where at least a portion of the layers of support structure 28 aregenerated pursuant to the support structure generation technique of thepresent disclosure (step 42).

In some embodiments, one or more of the layers of support structure 28may have a dense fill pattern and others of the layers may have a sparsefill pattern. The dense fill pattern refers to an interior fill of agiven layer in which the raster-fill pattern desirably reduces thenumber of voids within the layer. In comparison, the sparse fill patternrefers to an interior fill of a given layer in which the raster-fillpattern desirably creates voids within the layer to reduce the amount ofsupport material required to build the given layer. For example, thetop-most layers of support structure 28 (e.g., the top five layers) mayexhibit a dense fill arrangement to provide a suitable support surfacefor the overhanging layer of 3D model 26. Below these dense-filledlayers, support structure 28 may include sparse-filled layers. Asdiscussed below, the support structure generation technique of thepresent disclosure is desirably applied to the layers of supportstructure 28 having one or more sparse fill patterns. However, inalternative embodiments, the support structure generation technique maybe applied to any layer of a support structure (e.g., any layer ofsupport structure 28).

After support structure 28 is generated, computer 12 may select a firstlayer of the sliced layers and generate one or more contour tool pathsbased on the boundary or boundaries of the layer (step 44). In someexamples, a given layer may include multiple boundaries for buildingmultiple 3D models and support structures, and/or may include an outerboundary and an inner boundary for a single 3D model and/or supportstructure (e.g., having a hollow interior cavity).

The contour tool paths may be generated by computer 12 based on a roadwidth, which is a predicted width of a deposited road of the modeling orsupport material, and may depend on a variety of factors, such asmaterial properties, the type of deposition-based digital manufacturingsystem used, deposition conditions, deposition tip dimensions, and thelike. Suitable roads widths for use with system 10 range from about 250micrometers (about 10 mils) to about 1,020 micrometers (about 40 mils),with particularly suitable road widths ranging from about 380micrometers (about 15 mils) to about 760 micrometers (about 30 mils).

Computer 12 may then generate additional tool paths (e.g., raster paths)to bulk fill the interior region within the contour tool paths (step46), where the additional tool paths may also be based on the roadwidth. When the layer is completed, computer 12 may then determinewhether the current layer is the last of the sliced layers (step 48). Inthe current example, layer 36 is not the last layer. As such, computer12 may select the next layer (step 50) and repeat steps 74-82 until thelast layer is completed. When the last layer is completed, computer 12may transmit the resulting data to system 10 for building 3D model 26and support structure 28 (step 54). During the build operation,extrusion head 20 may then follow the patterns of the tool paths foreach layer.

FIG. 3 is a flow diagram of method 54 for generating a layer of asupport structure (e.g., support structure 28) pursuant to step 42 ofmethod 36 (shown in FIG. 2), and which is based on the support structuregeneration technique of the present disclosure. The following discussionof method 54 is also made with reference to 3D model 26 and supportstructure 28 (shown in FIG. 1). However, method 54 is also applicablefor building 3D models and corresponding support structures having avariety of different geometries.

As shown in FIG. 3, method 54 includes steps 56-71, and initiallyinvolves generating (or otherwise providing) one or more polygons thatinitially define the inner and/or outer boundaries of a given layer ofsupport structure 28 (step 56). The inner and outer boundary polygonsare each defined by a plurality of vertices that interconnect linearsegments, desirably in a closed-polygon arrangement.

Computer 12 may then generate a safety zone polygon around each interiorboundary polygon, if any, to reduce the risk of intersecting polygons ofthe inner and outer boundaries, as discussed below (step 58). In oneembodiment, each safety zone polygon may be generated as an outwardoffset from the vertices of an inner boundary polygon based on a “bufferwidth distance”. For example, the buffer width distance may be equal toa desired lateral air gap between 3D model 26 and support structure 28,and may also be increased by a factor of the road width of supportstructure 28 (e.g., twice the road width of support structure 28).

The vertices of the interior boundary polygon(s), if any, may also beoffset inward by a “first vertex travel distance” (step 60), where thefirst vertex travel distance is a maximum distance the vertices of theinterior boundary polygon(s) may be moved inward. This value desirablybalances the ability to decrease the dimensions of interior void regionsof support structure 28, while also providing suitable vertical supportfor above-overhanging layers. Accordingly, for slice heights of about250 micrometers (about 0.01 inches), examples of suitable values for thefirst vertex travel distance include up to about 50% of the road widthused to build support structure 28 with system 10, with particularlysuitable values ranging from about 15% to about 45% of the road width,and with even more particularly suitable values ranging from about 25%to about 40% of the road width. In some embodiment, the first vertextravel distance may be reduced for slice heights less than about 250micrometers (about 0.01 inches).

Computer 12 may also then determine a convex hull polygon for the outerboundary polygon (step 62). The convex hull polygon is the boundary ofthe minimal convex set containing a given non-empty finite set of pointsin the horizontal x-y plane for the outer boundary polygon. As discussedbelow, the convex hull polygon is beneficial for reducing the size andcomplexity of support structure 28.

Computer 12 may also determine whether the dimensions of the currentlayer, as defined by the outer boundary polygon, are greater than one ormore minimum thresholds (step 64). For example, in step 64 of method 54,computer 12 may determine a characteristic width of the outer boundaryto identify any thin-wall regions of the outer boundary polygon.Computer 12 may compare the characteristic width to a “minimum widththreshold”. The use of the minimum width threshold is beneficial toprevent the given layer of support structure 28 from becoming too thinto be stable. Examples of suitable values for the minimum widththreshold range from about 500 micrometers (about 0.02 inches) to about2,500 micrometers (about 0.1 inches), with particularly suitable valuesranging from about 500 micrometers (about 0.02 inches) to about 1,300micrometers (about 0.05 inches). In some embodiments, the minimum widththreshold may also scale with the vertical height of 3D model 26 if thevertical height exceeds a particular level (e.g., greater than about 300millimeters (about 12 inches)).

Additionally, computer 12 may compare the area defined by the outerboundary polygon to a “minimum area threshold”. For example, the minimumthreshold area may be determined as the difference between the areadefined by the outer boundary polygon and the combined areas defined bythe offset inner boundary polygon(s). The use of the minimum areathreshold is beneficial to ensure that a minimum horizontal area isretained for supporting above layers. Examples of suitable values forthe minimum area threshold range from about 130 square millimeters(about 0.2 square inches) to about 650 square millimeters (about 1.0square inch), with particularly suitable values ranging from about 130square millimeters (about 0.2 square inches) to about 320 squaremillimeters (about 0.5 square inches). In some embodiments, the minimumarea threshold may also scale with the area of a two-dimensional,horizontal bounding box of 3D model 26 if the area of the bounding boxexceeds a particular level (e.g., greater than about 650 squarecentimeters (about 100 square inches)).

As further shown in FIG. 3, if one or more of the dimensions do notexceed their respective minimum thresholds, computer 12 may then omitstep 66 of method 54, and may proceed directly to step 68.Alternatively, if the dimensions do exceed their respective minimumthresholds, then computer 12 may offset the convex hull polygon inwardby a “second vertex travel distance” (step 66), which defines a maximumdistance the vertices of the outer boundary may be moved inward. Thisvalue desirably balances the ability to decrease the dimensions of theouter boundary polygon with the ability to provide suitable verticalsupport for above-overhanging layers. Accordingly, for slice heights ofabout 250 micrometers (about 0.01 inches), examples of suitable valuesfor the second vertex travel distance include those discussed above forthe first vertex travel distance. In some embodiments, the second vertextravel distance may also be reduced for slice heights less than about250 micrometers (about 0.01 inches). In additional embodiments, thefirst vertex travel distance and the second vertex travel distance maybe the same or substantially the same values.

Computer 12 may then offset the vertices of the outer boundary polygonoutward by a “third vertex travel distance” (step 68), where the thirdvertex travel distance is desirably the same or substantially the sameas the second vertex travel distance. Offsetting the vertices of theouter boundary polygon outward in this step incrementally evolves theoriginal outer boundary polygon toward the offset convex hull. It hasthe effect of making non-convex regions of the outer boundary polygonmove toward the offset convex hull, or even removing them entirely, suchas in the case of long, narrow cutouts.

Computer 12 may then intersect the region of the offset outer boundarypolygon with the region of the offset convex hull polygon (step 70). Asdiscussed below, intersecting the offset outer boundary polygon with theoffset convex hull polygon in this manner results in a new outerboundary polygon that has its maximum vertices defined by the offsethull convex polygon and its minimum vertices defined by the offset outerboundary polygon, and is referred to as an intersection outer boundarypolygon.

Accordingly, as discussed below, at least a portion of the vertices ofthe resulting intersection outer boundary polygon may include (1) one ormore vertices created at the intersections of the offset convex hullpolygon and the offset outer boundary polygon, (2) one or more verticesof the offset convex hull polygon that are located inside of the offsetouter boundary polygon, (3) one or more vertices of the offset outerboundary polygon that are located inside of the offset convex hullpolygon, and combinations thereof. This allows segments of the offsetouter boundary polygon, located inside the offset convex hull polygon,to move outward the third vertex travel distance, thereby reducing thecomplexity of the successive layers of support structure 28.

In some situations, the polygons of the offset outer boundary and theoffset convex hull may not necessarily intersect. However, the regionsdefined by the offset outer boundary polygon and the offset convex hullpolygon will intersect. For example, in situations where the originalouter boundary polygon already exhibits convex dimensions, thedetermined convex hull (from step 62) may be co-linear with outerboundary polygon. Thus, the inward offsetting of the convex hull polygonand the outward offsetting of the outer boundary polygon, respectivelypursuant to steps 66 and 68, will result in the offset convex fullpolygon being entirely inside the region of the offset outer boundarypolygon. In these example situations, the vertices of the intersectionouter boundary polygon will be based entirely on (2) the vertices of theoffset convex hull polygon that are located inside of the offset outerboundary polygon, subject to the safety zone polygon, as discussedbelow.

Computer 12 may also unite the vertices of the intersection outerboundary polygon may with the safety zone polygon (step 71). Thisresults in the intersection outer boundary polygon having its minimumvertices also defined at least in part by the safety zone polygon, as isreferred to as a united outer boundary polygon. As discussed above, thisincrementally evolves the original outer boundary polygon toward theoffset convex hull. Accordingly, as discussed below, at least one of thevertices of the united outer boundary polygon may also include (1) oneor more vertices created at the intersections of the offset outerboundary polygon and the safety zone polygon, (2) one or more verticesof the safety zone polygon located inside of the offset outer boundarypolygon, and combinations thereof.

After step 71 of method 54 is completed, computer 12 may then generatecontour tool paths based on the united outer boundary polygon and on anyoffset inner polygon(s), and may fill interior region(s) with one ormore raster tool paths (e.g., sparse-fill raster tool paths), pursuantto steps 44 and 46 of method 36 (shown in FIG. 2). In some embodimentsthat include multiple support structures, method 54 may be applied toeach support structure, where adjacent support structures may also jointogether due to the incremental evolution of the convex dimensions.Method 54 may then be repeated for each subsequent layer downward alongthe vertical z-axis, where each subsequently lower layer is generated tosupport the previously generated layer, as modified by method 54.

While steps 56-70 of method 54 are shown and described in a particularorder, the various steps of method 54 may alternatively be performed ina variety of different orders so long as the reordering of a particularstep does not prevent the operation of a subsequent step. Furthermore,an alternative embodiment, steps 58 and 71 may be omitted, such thatcomputer 12 may then generate contour tool paths based on theintersection outer boundary polygon (from step 70) and on any offsetinner polygon(s). Moreover, in additional alternative embodiments, suchas in embodiments in which support structure 28 does not includeinterior void regions, steps 58, 60, and 71 may be omitted. Accordingly,computer 12 may generate the contour tool paths based on the unitedouter boundary polygon and/or on the intersection outer boundarypolygon, in addition to any offset inner polygon(s), such that thecontour tool path(s) are generated based at least in part on theintersection outer boundary polygon.

FIGS. 4A-4H, 5A-5H, and 6A-6H illustrate the application of method 54(shown in FIG. 3) to layers 28 a-28 c of support structure 28, wherelayer 28 a (shown in FIGS. 4A-4H) is a top-most, sparse filled layer ofsupport structure 28, layer 28 b (shown in FIGS. 5A-5H) is the layerdirectly below layer 28 a, and layer 28 c (shown in FIGS. 6A-6H) is thelayer directly below layer 28 b. As shown in FIG. 4A, layer 28 aincludes a pair of polygons that define outer boundary 72 and innerboundary 74, where outer boundary 72 and inner boundary 74 are eachpolygons defined by a plurality of segment-interconnected vertices.Accordingly, pursuant to step 56 of method 54, computer 12 may generateouter boundary 72 and inner boundary 74 based on one or moreconventional support generation algorithms.

As shown in FIG. 4B, pursuant to step 58, computer 12 may then generatesafety zone 76 around inner boundary 74, where safety zone 76 is anadditional polygon generated as an outward offset from the vertices ofinner boundary 74 based on the buffer width distance. As used herein,directional terms such as “inward”, “outward”, and the like, refer todirections relative to a polygon. For example, a direction that isoffset outward from a polygon refers to an offset that is outside of andaway from the polygon, such as safety zone 76 being at an outward offsetfrom inner boundary 74, as shown in FIG. 4B. Similarly, a direction thatis offset inward from a polygon refers to an offset that is inside ofand away from the polygon.

As shown in FIG. 4C, pursuant to step 60, computer 12 may offset thevertices of inner boundary 74 inward by the first vertex travel distanceto attain the polygon of offset inner boundary 78, and the originallygenerated inner boundary 74 (shown in FIG. 4C with broken lines) may bediscarded.

As shown in FIG. 4D, pursuant to step 62, computer 12 may then generateconvex hull 80, which, as shown, is a polygon of the minimal convex setcontaining a given non-empty finite set of points in the horizontal x-yplane of outer boundary 72. Computer 12 may then determine whether thedimensions of outer boundary 72 are greater than one or more minimumthresholds, pursuant to step 64. In the current example, thecharacteristic width are respectively greater than the minimum widththreshold and the minimum area threshold.

Accordingly, as shown in FIG. 4E, computer 12 may then proceed to step66 and may offset convex hull 80 inward by the second vertex traveldistance, where, as discussed above, is a maximum distance that thevertices of outer boundary 72 may be moved inward. This provides thepolygon of offset convex hull 82, and the originally generated convexhull 80 (shown in FIG. 4E with broken lines) may be discarded. As shownin FIG. 4F, computer 12 may then proceed to step 68 and may offset outerboundary 72 outward by the third vertex travel distance to attain thepolygon of offset outer boundary 84. The originally generated outerboundary 72 (shown in FIG. 4F with broken lines) may correspondingly bediscarded. While offset outer boundary 84 is illustrated in FIG. 4E withsharp corners at its vertices, in some embodiments, the outwardoffsetting of the vertices of outer boundary 72 may create roundedcorners, where the locus of the vertex points may be equidistant fromoriginal polygon (i.e., from outer boundary 72).

As shown in FIG. 4G, pursuant to step 70, computer 12 may intersectoffset outer boundary 84 with offset convex hull 82 and safety zone 76to attain the polygon of intersection outer boundary 86. The offsetouter boundary 84 (shown in FIG. 4G with broken lines) maycorrespondingly be discarded. In the shown example, offset outerboundary 84 may intersect with offset convex hull 82 such thatintersection outer boundary 86 has its maximum vertices defined by theoffset convex hull 82 and its minimum vertices defined by offset outerboundary 84.

Accordingly, the vertices of intersection outer boundary 86 include (1)vertices 88 created at the intersections of offset convex hull 82 andoffset outer boundary 84, (2) the vertices 90 of offset convex hull 82that are located inside of offset outer boundary 84, and (3) thevertices 92 of offset outer boundary 84 that are located inside ofoffset convex hull 82. As discussed above, this allows the segments ofoffset outer boundary 84 located inside offset convex hull 82, to moveoutward, thereby reducing the complexity of the successive layers ofsupport structure 28.

This intersecting of offset convex hull 82 and offset outer boundary 84may also be visualized by identifying the points along offset convexhull 82 where offset outer boundary 84 intersects offset convex hull 82,and eliminating any segment portions of offset outer boundary 84 thatextend outside of offset convex hull 82 beyond the intersection points,and also eliminating any segment portions of offset convex hull 82 thatextend inside of offset outer boundary 84 beyond the intersectionpoints.

In current example, outer boundary 72 (shown in FIGS. 4A-4F) is notco-linear with convex hull 80 (shown in FIGS. 4D and 4E). As such, asshown in FIG. 4G, the polygons of offset convex hull 82 and offset outerboundary 84 intersect at vertices 88. Alternatively, in an example inwhich outer boundary 72 was co-linear with convex hull 80, offset convexhull 82 would be located entirely within offset outer boundary 84. Asdiscussed above, in this alternative example, the vertices ofintersection outer boundary 86 would be derived entirely from vertices90 of offset convex hull 82. Accordingly, method 54 is suitable forcontinuing to modify layers in which the outer boundaries of the layersalready exhibit convex dimensions.

As further shown in FIG. 4G, in the current example, offset outerboundary 84 does not overlap safety zone 76. As such, pursuant to step71 of method 54, the resulting united outer boundary has the samesegments and vertices as intersection outer boundary 86 (i.e., there areno segments of offset outer boundary 84 that unite with safety zone 76).Alternatively, in an example in which intersection outer boundary 86included segment 94 extending inside of safety zone 76, the resultingunited outer boundary from step 71 of method 54 would then also havevertices 96 created at the intersections of intersection outer boundary86 and safety zone 76, and vertex 98 of safety zone 76 that is locatedoutside of intersection outer boundary 86. Accordingly, the resultingpolygon of the united outer boundary would include the portions ofsegment 94 extending toward vertices 96, and the segments betweenvertices 96 and 98. As discussed above, the use of safety zone 76 inthis manner maintains a minimum distance between offset inner boundary78 and intersection outer boundary 86, where, in the current example,the minimum distance may be the sum of the buffer width distance and thefirst vertex travel distance.

As shown in FIG. 4H, safety zone 76 and offset convex hull 82 may thenbe discarded to provide the resulting layer 28 a having the polygons ofoffset inner boundary 78 and intersection outer boundary 86. Method 54may then be repeated for each subsequent layer below layer 28 a, wherethe initial outer and inner boundary polygons may be generated (pursuantto step 56 of method 54) to support the previous modified layer ofsupport structure 28. For example, as shown in FIG. 5A, layer 28 b isinitially generated to support the resulting layer 28 a having offsetinner boundary 78 and intersection outer boundary 86, as shown in FIG.4H. Accordingly, as shown in FIGS. 5A-5H, computer 12 may apply method54 to layer 28 b following the same process discussed above for layer 28a, where the respective reference numbers are increased by “100”.

Furthermore, as shown in FIG. 6A, layer 28 c is initially generated tosupport the resulting layer 28 b having offset inner boundary 178 andintersection outer boundary 186, as shown in FIG. 5H. Accordingly, asshown in FIGS. 6A-6H, computer 12 may also apply method 54 to layer 28 cfollowing the same process discussed above for layer 28 a, where therespective reference numbers are increased by “200”.

A comparison of intersect outer boundaries 86, 186, and 286 illustratesthe effects of method 54 on the generation of successive layers ofsupport structure 28. For example, as discussed above, method 54 reducesthe area of layers 28 a-28 c in the horizontal x-y plane in a downwarddirection along the vertical z-axis. This reduces the amount of supportmaterial required to build support structure 28, and reduces thedistance that extrusion head 20 is required to move around the lateralperimeter of a given layer of support structure 28, and as well aslowering the required total angular deflection of extrusion head 20, asdiscussed above.

Additionally, the interior void in support structure 28, as defined inpart by offset inner boundaries 78, 178, and 278, also decreases in adownward direction along the vertical z-axis. This reduces interruptionswhen bulk filling the interior regions of the support structure (e.g.,with a raster fill pattern), which further reduces the overall timerequired to build support structure 28 with system 10. In oneembodiment, computer 12 may also eliminate the inner boundary polygonwhen the inner boundary polygon eventually becomes too small due to thedecrease in its size over successive layers. Computer 12 may continue toapply method 54 to each successive layer of support structure 12 untilthe last layer is reached (pursuant to step 48 of method 36, shown inFIG. 2). Computer 12 may then transmit the resulting data to system 10to build 3D model 26 and support structure 28, where support structure28 includes the outer convex dimensions that reduce in size andcomplexity in a downward direction along the vertical z-axis.

Although the present disclosure has been described with respect toseveral embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the disclosure.

1. A computer-implemented method for generating data for a supportstructure to be built with a deposition-based digital manufacturingsystem, the method comprising: providing a boundary polygon of a layerof the support structure; generating a convex hull polygon based on theboundary polygon; offsetting the convex hull polygon inward; offsettingthe boundary polygon outward; and generating an intersection boundarypolygon based at least in part on the offset boundary polygon and theoffset convex hull polygon.
 2. The method of claim 1, wherein offsettingthe convex hull polygon inward comprises offsetting the convex hullpolygon inward by a distance that includes up to about 50% of a roadwidth for building the support structure with the deposition-baseddigital manufacturing system.
 3. The method of claim 1, whereinoffsetting the boundary polygon outward comprises offsetting theboundary polygon outward by a distance that includes up to about 50% ofa road width for building the support structure with thedeposition-based digital manufacturing system.
 4. The method of claim 1,wherein the layer of the support structure further includes an innerboundary polygon, and wherein the method further comprises offsettingthe inner boundary polygon inward.
 5. The method of claim 1, wherein thelayer of the support structure further includes an inner boundarypolygon, and wherein the method further comprises generating a safetyzone polygon at a location that is offset outward from the innerboundary polygon.
 6. The method of claim 5, and further comprisinguniting the generated intersection boundary polygon with the safety zonepolygon.
 7. The method of claim 1, and further comprising comparing anarea of the offset boundary polygon to a minimum area threshold.
 8. Acomputer-implemented method for generating data for a support structureto be built with a deposition-based digital manufacturing system, themethod comprising: providing vertices defining a boundary polygon for alayer of the support structure; generating vertices of a convex hullpolygon based on the vertices of the boundary polygon; offsetting thevertices of the convex hull polygon inward to provide an offset convexhull polygon; offsetting the vertices of the boundary polygon outward toprovide an offset boundary polygon; and generating an intersectionboundary polygon having vertices, wherein at least a portion of thevertices of the intersection boundary polygon are selected from thegroup consisting of a vertex that is located at an intersection of theoffset boundary polygon and the offset convex hull polygon, a vertex ofthe offset boundary polygon located inside of the offset convex hullpolygon, a vertex of the offset convex hull polygon located inside ofthe offset boundary polygon, and combinations thereof.
 9. The method ofclaim 8, wherein the vertices of the convex hull polygon are offsetinward by a distance up to about 50% of a road width for building thesupport structure with the deposition-based digital manufacturingsystem.
 10. The method of claim 8, wherein the boundary polygon is afirst boundary polygon, and wherein the method further comprises:generating vertices defining a second boundary polygon for the layer ofthe support structure; and offsetting the second boundary polygoninward.
 11. The method of claim 8, wherein the boundary polygon is afirst boundary polygon, and wherein the method further comprises:generating vertices defining a second boundary polygon for the layer ofthe support structure; and generating vertices of a safety zone polygonthat are offset outward from the second boundary polygon.
 12. The methodof claim 11, wherein at least one of the vertices of the intersectionboundary polygon is selected from the group consisting of a vertex thatis located at an intersection of the offset boundary polygon and thesafety zone polygon, a vertex of the safety zone polygon located insideof the offset boundary polygon, and combinations thereof.
 13. The methodof claim 11, wherein the generated vertices of the safety zone polygonare offset outward from the second boundary polygon by a distance thatis based at least in part of a road width for building the supportstructure with the deposition-based digital manufacturing system. 14.The method of claim 8, and further comprising generating a tool pathbased at least in part on the intersection boundary polygon.
 15. Amethod for building a support structure with a deposition-based digitalmanufacturing system, the method comprising: generating a convex hullpolygon based on a boundary polygon for each of a plurality of layers ofthe support structure; offsetting the convex hull polygon inward foreach of the plurality of layers; offsetting the boundary polygon outwardfor each of the plurality of layers; generating an insert boundarypolygon for each of the plurality of layers based at least in part onthe offset boundary polygon and the offset convex hull; and generating atool path for each of the plurality of layers based at least in part onthe insert boundary polygon; transmitting the generated tool paths tothe deposition-based digital manufacturing system; and building thesupport structure based at least in part on the transmitted tool paths,wherein the support structure has substantially convex dimensions. 16.The method of claim 15, wherein the convex hull polygon is offset inwardfor each of the plurality of layers by a distance that includes up toabout 50% of a road width used to build the support structure with thedeposition-based digital manufacturing system.
 17. The method of claim16, wherein the distance ranges from about 15% of the road width toabout 45% of the road width.
 18. The method of claim 15, wherein atleast one of the layers further includes an inner boundary polygon, andwherein the method further comprises generating a safety zone polygonoffset from the inner boundary polygon in an outward direction.
 19. Themethod of claim 18, and further comprising uniting at least one of theoffset boundary polygons with the safety zone polygon.
 20. The method ofclaim 15, and further comprising comparing an area of the offsetboundary polygon to a minimum area threshold for at least a portion ofthe layers.